Unless otherwise indicated, the foregoing is not admitted to be prior art to the claims recited herein and should not be construed as such.
Modern portable applications may require power management devices that connect directly to Li-ion batteries. Such configurations can subject the sensitive circuits of the power management devices to voltages of 4.8V or higher. In 28 nm CMOS technologies, standard IO devices can have a maximum rating (Vmax) of about 2.3V. Higher voltage devices with Vmax of 5V can be fabricated in 28 nm technology, but at significantly higher mask costs and incurring power efficiency degradation. Vmax typically refers to the gate-source voltage (Vgs) or gate-drain voltage (Vgd) of the device.
Merely to illustrate this point, FIG. 4 shows an example of a power stage using 28 nm technology FETs. For this example, suppose Vmax is 2.3V and the input voltage Vin is 3×Vmax. The output Vout of the power stage will therefore swing from 0V to 3×Vmax. The gates of Q1 and Q2 may be driven by a gate driver; for example, a switching power supply, a Class D amplifier, etc. FIG. 4 shows a configuration of a switching supply in which the power stage outputs 3×Vmax. In order for Vout to output 3×Vmax, the gate of Q2 needs to be grounded in order to turn OFF Q2 (the gate of Q1 is driven to 2×Vmax in order to turn ON Q1). However, driving the gate of device Q2 to ground when its drain is at 3×Vmax creates a condition where Vgd of Q2 exceeds its Vmax rating, which over time can break down the gate oxide layer.